Optical disk devices are used for the storage of computer-prepared data and have recognized value in their ability to store large quantities of data. The media for use in such devices is reactive to the intensity modulation of light, such as may be produced by the rapid switching of a semi-conductor laser. In order to write data on optical media, the laser power must be controlled at a relatively high power level, in order that the media can be altered in accordance with the input data stream. In reading the data back, the laser power level is controlled to a lower level so that the media is not altered by the laser beam but the reflected light indicates the presence or absence of media alterations, that is, digits of data caused by the input data stream.
Optical media is of two general types, media which can be written only once and media which can be written, erased, and written again. Write-once media (WORM) is permanently altered when write power levels are produced by the laser beam. Erasable media, such as magneto-optic (MO) media, is not permanently altered when data is written. In the MO media, the magnetic orientation of the reactive material is altered in the writing process, and in the erasing process, the magnetic orientation is reordered.
When reading MO data from an optical disk, the reflected light beam is passed through optical elements such as a quarter wave-plate and a polarizing beam splitter to separate the reflected beam into P and S polarization components. The balance in the amplitude of the P and S beam components is affected by the magnetic orientation of the MO media, which rotates the linear polarization of the reflected light beam in accordance with the well-known Kerr effect. By sensing the light amplitudes of the P and S beam components, the magnetic orientation of the media is sensed thereby enabling the generation of an MO data signal in accordance with the magnetic orientation present in the media. For example, the light amplitude of the two beams may produce a first value for a first magnetic domain orientation representing a "zero" bit, and a second value for a reverse magnetic domain orientation representing a "one" bit. There are other types of encoding schemes; some use transitions from one state to another as a "bit."
Before MO media can be written, it should be erased, that is, all magnetic domains should have the same orientation. That is accomplished within playback/recording apparatus by placing a bias coil in close juxtaposition with the media. Thereafter, the entire optical disk is heated by the laser to a level sufficient to enable a bias field generated by the bias coil to orient the magnetic domains within the optical media in the same direction. That direction is then considered to represent a "zero" bit.
In order to write "one" bits on the optical media, the bias coil is again placed into close juxtaposition with the media. At each spot on the optical disk at which it is desired to write a "one" bit, the laser is energized to heat that spot to an elevated level sufficient to enable a bias field generated by the bias coil to reverse the magnetic orientation of that spot on the media. The reverse orientation is a result of applying current to the bias coil in a reverse direction from that used in erasing the disk such that the magnetic field produced by the bias coil is reversed. In that manner, the orientation of the magnetic domains at the spot heated by the laser is reversed.
For write-once media, data is read back by reflecting a light beam from the surface of the disk. The reflected light beam is intensity-modulated by the permanent condition of the disk and by detecting the intensity of the reflected light beam, a signal is generated in accordance with the WORM data.
There are various types of WORM media. One type requires the burning away of a reflective surface by a laser beam at those spots at which "one" digits are to be written. As a consequence, when reading such media, light is reflected with significant intensity from those areas which have not been altered by the laser and with much less intensity from those spots at which the reflective surface is removed. When the intensity of the reflected light is detected at a low level, the detecting apparatus interprets a "one" bit. When the intensity is high, the detecting apparatus interprets a "zero" bit.
The American National Standards Institute (ANSI) has developed cartridges with standard dimensions for holding recording media. In that manner the manufacturers of cartridges and the manufacturers of recording/playback apparatus (drives) have the capability of developing their respective products for use with a variety of other manufacturers products. The standard cartridge includes datum features, for example, locating holes, that are designed to mate with datum features in a drive, for example locating pins, to accurately position the cartridge within the drive. Holding features in the cartridge such as notches and recesses, are dimensioned relative to the datum features. After insertion of a cartridge into a drive, the notches are typically used to hold the cartridge while it is loaded onto the locating pins and simultaneously loaded onto the drive spindle.
Standards have been developed for 130 mm (5.25 inch) optical disk drives and cartridges, and other standards have been developed for 90 mm (3.5 inch) optical disk drives and cartridges. These standards, unfortunately, have not been developed to allow upward compatibility so that the smaller diameter cartridge can be easily used within a drive designed for a larger diameter cartridge.
The 90 mm cartridge is much smaller than the 130 mm cartridge. This difference prevents a loader mechanism designed for a 130 mm cartridge from accepting a 90 mm cartridge unless the mechanism is extensively modified, resulting in a much more complex and costly design. The aperture in the 90 mm cartridge, which provides access to the disk hub by the spindle motor, is smaller than the disk hub and spindle motor hub defined by 130 mm standards. As a result, a spindle hub designed to drive a 130 mm disk cannot fit into the aperture of the 90 mm cartridge to make contact with the disk hub.
It is, therefore, an object of this invention to provide an adaptor cartridge to resolve the compatibility problem without any impact on the loader mechanism or spindle motor of the 130 mm optical disk drive. Accomplishment of that task enables the insertion of a 90 mm disk into a position in which data on the disk can be read by the 130 mm drive apparatus. Also, in the case of WORM media, the 90 mm WORM disk could be written by the 130 mm apparatus.
Even though the ability of placing a 90 mm optical disk and cartridge into a 130 mm form factor optical drive is a desirable feature, it is still not possible to write data on an MO disk unless a bias field can be applied to the disk. Since the large bias coil in a drive designed for 130 mm optical disk and cartridge cannot fit into the smaller opening of a 90 mm cartridge, provision must be made for providing the necessary bias field in some other manner.
It is therefore another object of this invention to provide a magnet in the adaptor cartridge so that the ability to write MO media is included in the adaptor cartridge.